Hydraulic brake system



Dec. 22, 1936: w. F. oLlvER Er AL HYDRAULIC BRAKE SYSTEM Filed July 11,1952 2 Shets-Sheet 1 afirme De@ 22; 19:16.r

w. F. OLIVER |=:r` AL HYDRAULIC BRAKE SYSTEM Filed July 11, 1952 2sheets-Sheet 2 Patented Dec. 22, 1936 PAT-ENT OFFICE HYDRAULIC BRAKESYSTEM Wallace F. Oliver, Herbert C. Bowen,.and Erwin F. Loweke,Detroit, Mich., assignors to Hydraulic Brake Company, Detroit, Mich., acorporation of California Application July 11, 1932, Serial No. 621,906

` 23 Claims.

Our invention pertains to hydraulic brake sys` tenis and is particularlyconcerned with an improved hydraulic brake system for automotivevehicles, although certain features of our invention are capable ofapplication in other fields.

In hydraulic brake systems it -is of the utmost importance that theconduits, wheel cylinders and master cylinder be completely lled with anincompressible body of -liquid for transmitting without loss thevpressure applied on the foot pedal tothe brake. shoes at the vehiclewheels.

It sometimes happens in brake systems which have been used over longperiods of time that the sealing means at the Wheel cylinders becomesworn to such an extent as to permit minute quantities of air to leakpast the pistons atthe Wheel cylinders. These quantities of air areusually so small that they will not affect the operation of the brakesystem if the brakesystem is designed promptly to cleanse itself of suchconduit system. Such volatilization of the brake uid is undesirable asunder certain circumstances it may seriously aiect the operation of thebrake system.

An object of our invention is to provide a new and novel brake systemwhich Will automatically cleanse itself of any airwhich may nd its wayintol the system.

Another object is to provide a brake system which will facilitatecooling of the. brake mud. Another object is to provide novel designs ofwheel cylinders, Wheel cylinder pistons, and conduit arrangements forcarrying out the above described objects.

Other objects and advantages will become apparent as the descriptionproceeds.

In the drawings, Fig. 1 is a plan View of a part of the chassis of anautomotive vehicle, showing one form of our brake system appliedthereto;

Fig. 2 is a sectionalielevation through one of the wheel cylinders, andshows some of the mechanism immediately adjacent the wheel cylinders;

Fig. 3 is a section taken on the line`3-3 of Fig. 2; 55 Fig. 4 is-asectional view through the valve ,On thisframe is mounted a combinedmaster (Cl. v18S-152) mechanism mounted 'at the discharge end of theVmaster cylinder;

Fig. 5 is a diagrammatic view of the embodiment of our invention shownin Fig. 1;

Fig. 6.is a diagrammatic view similar to Fig. 5, 5 but showing adifferent embodiment of our in'- vention;

Fig. 7 is 'a sectional View through one of the wheel cylinders used inthe embodiment shown in Fig. 6; 10

Fig. 8 is a sectional view through a wheel cylinder which is identicalwith the wheel cylinder shown in Fig. 7 but illustrating a diierentapplication for such wheel cylinder, and

lFig'. 9 is a sectional View through a two-diam- 15 eter wheel cylinder.

.Referring first to that embodiment of our invention illustrated inFigs. 1 to 5, inclusive, we have shown the frame andv running gear of aconventional automobile in dotted lines in Fig. 1. 20

cylinder and reservoir unit I0 which may be of any conventional ordesired type, but which preferably is generally similar to thatdisclosed in v Malcolm Loughead and Erwin F. Loweke Patent No.1,758,671, of May 1.3, 1930, except that the valve mechanism designatedby the reference numerals 3 I to 3l, inclusive, in said patent, isomitted.

This master cylinder and reservoir unit comprises in general a uidreservoir containing a 'master cylinder.|2 having a piston I3reciprocated by van arm I4 niounted on an oscillable shaft I5 whichextends outside of the reservoir for connection with the usual brakepedal I6. 3 The arm I4 has a separable connection with the piston I3,the latter being returned by a spring I 'I, whereasthe brake pedal I6 isreturned by a separate spring I6a (Fig. 5). When the piston I3 is inretracted position it uncovers a port I3a 40 which provides freecommunication between the cylinder I2 and the interior of the reservoirI I. The rear end of the reservoir II is provided with a boss I8 intowhich is threaded a bolt I9 having a T-shaped conduit 20 bored therein.

A valve-carrying member 2I is clamped between the boss I8'and the headof the bolt I9. The member 2l has a valve chamber 22 containing a valve23 which normally closes communication between the `chamber 22 and theT-shaped conduit 20 in the bolt I9. The T-shaped conduit 20 is in opencommunication with the discharge end of the master cylinder I2 throughthe medium of passageway 26.

When the drlverof the vehicle applies the 56 brakes, the fluiddischarged from the mastercylinder forces the Valve 23 Aaway from itsseat 25 against the tension of valve spring 26,- and the fluid thusforced past the valve passes through tubular fitting 21 and thence intothe conduit 28, which, in the present embodiment, is shown as extendingrearwardly along the left-hand channel member of the vehicle frame to aT29 located approximately over the rear axle of the vehicle.

A flexible hose 30 leads from the side outlet of the T 29 to inletnipple l3| of Wheel cylinder 32. This wheel cylinder is shown mostclearly in Figs. 2 and 3, and includes a casting 34 having bossesthreaded'to receive bolts 36 by means .of which the wheel cylinder isaffixed to the usual supporting pan 31. The casting 34 is provided witha cylindrical bore 38 which communicates with the nipple 3| by means ofa passageway 39.

A second passageway 40 connects the cylinder bore with a bleeder screw4| which may lbe of any conventional type but which, in the presentinstance, is shown as comprising a tubular sleeve 42 threaded into thecasting., 34, and a valve member 43 having a tapered inner end ywhich innormal position closes the passageway 4|l.`

' When it is desired to bleed air out of the wheel cylinder the valvemember 43 is unscrewed sufficiently to withdraw its tapered end fromsealing -ngagement with thev passageway 4D, whereupon air may pa'ssthrough the passageway 40, enter the cross openings 44, and -thence intoa passageway extending longitudinally of the valve member 43 whichlcommunicates with atmosphere.

While the pistons used in the wheel cylinder 32 may be of anyconventional type, we preferably use pistons of the type indicated at 45in Fig. 2. Such pistons'have plane faces which are normally held inengagement by retractile springs 46 (Fig. 5)'. 'Ihe plane faces of thepistons 45 merge into beveled surfaces 41 which form an annular groovefor distributing `fluid under pressure supplied to passageway 39.

It is to be understood that the abutting faces of the pistons are notmachined so accurately as to prevent relatively free access of fluidbetween said faces, so that when fluid pressure is applied the fluidpressure acts over the entire faces of the pistons 45.

Each piston 45 is provided with an annular recess 48 in which islocateda. rubber ring 49, this rubber ring being -U-shaped incross-section. Each piston 45 is further provided with a tapered recess50 for receiving one end of aplston rod 5|,

the other end of which has an adjustable threaded connection with asocket member 52 which in turn contacts witha brake shoe 53.

AA coarse-toothed wheel 54 is associated With member and thencealongthis cross member to the opposite side of the frame, whence thisconduit connects with a second T 59.

A flexible hose 80 connects the T 59 with n.

second wheel cylinder 32a which may be identivc al 4with the wheel.cylinder 32 previously described. Conduit 6| connects T 59 with T 62which in .turn is connected to a third wheel cylinder 32h by a flexiblehose 63.

T 62 is preferably located approximately at the point where a crossmember connects the side members of the vehicle frame, and a conduit 64extends along this cross member and connects T 62 with T 65, which inturn is connected to a vfourthwheel cylinder 32e by aflexiblc hose 6 6.

The wheel cylinders 32h and 32e may likewise be identical with the wheelcylinder'38 first deto 5. inclusive, the conduits 2a, 5s, sl, s4 and' 61form a complete circuit. The fluid discharged from the master cylinderis forced past the valve 23 and into conduit 28, whence this fluid flowsin the direction of the arrows toward the T 29. The check valve 69prevents any of the fluid discharged by the master cylinder from'flowing directly into the conduit 61.

When the pistons in the wheel cylinders are returned to theirnormalpositions by retractile springs, the fluid returned to 'theseconduits by the wheel cylinders tends to flow in the direction of thearrows and is forced past check valve 69 and thence returns to themaster cylinder. 'I'he tendency thus is for the fluid to travel in acircular path, and -the same fluid is not repeatedly forced into theWheel cylinders. The check valve 69 retains in the conduits and wheelcylinders a predetermined fluid pressure which prevents infiltration ofair.

The pistons 45 are so designed that when the pistons are in the normalposition shown in Fig. 2, there is a minimum of fluid left in thecylinder,

so that during the return stroke of the pistons 45 practically all ofthe fluid which was in the cylinder when the brakes were applied is dis`charged by the return stroke of the wheel cylinder pistons.

It should valso be pointed out that the flexible vhoses which connectthe wheel cylinders with the conduit system on the frame of the vehiclehave at present an internal diameter of only one-eighth inch so thatthe'volume of fluid retained in each-hose is .small compared t'o thelcapacity of its wheel cylinder, wherefore, upon each application of thebrakes, several times the,

volume of fluid contained in 'a flexible hose is forced into and out ofits associated wheel cylinder, thereby completely changing the fluid inthe hose.'

As previously pointed out, the brake shoes,

brake drums, wheel cylinders, and associated' parts, become hot duringa. long application of the brakes, and thisheat is communicated to thefluid in the wheel cylinders, sometimes raising the temperature of thisfluid to such an cxtent as to volatilize one of the constituents there-lof. Upon a release of the brakes practically all of this hot fluidis'discharged from the wheel cylinders into the conduits 58, 6|, 64 and61,

l not passback into such wheel cylinder upon the next application of thebrakes b moves on toward the next wheel cylinder in the circuit, butbefore the fluid just discharged from one wheel cylinder can reach thenext wheel cylinder, such iluid will have to pass through a considerablelength of relatively cool copper conduit, and in'so travelling from onewheel cylinder to the next, the temperature of the uld will be greatlyreduced.

The closed conduit circuit on the frame of the vehicle is normallylocated above the wheel cylinders so that the flexible hoses leadupwardly from the wheel cylinders to these conduits. Therefore any airwhich may find its way into a wheel cylinder can travel upwardly throughthe ilexible conduit and into the copper conduits on the 4vehicle frame.Upon the next application of the brakes these minute quantities of airwill be ad vanced around the conduit circuit until they eventually reachthe master cylinder, from whence they pass into the reservoir and thenceto atmosphere. In this manner the system quickly clears itselfof the airand maintains itself in a conduit of maximum efllciency. 'I'hisautomatic scavenging of air is also much facilitated by the particulardesign of wheel cylinders whereby practically all of the fluid and anyair bubbles which may collect therein are discharged from thewheel'cylinders during the return strokes of the wheel cylinder pistons.

` In the normal operation of the wheel cylinder shown in Figure 3, anytrifling amount of air which might leak into the cylinder during itsnormal use would be carried out of the cylinder by the fluid dischargedtherefrom by the return of the wheel cylinder pistons following eachapplication of the brakes. When it is desired to bleed the system, thebleed screw 83 at one of the wheel cylinders is opened. During thebleeding operation, however, the' wheel cylinder pistons remain idle andilud is pumped into the wheel cylinder 38 rapidly through the inlet 39,thereby preventing escape of air through this inlet during thel bleedingoperation. The excess of fluid which is thus pumped into the wheelcylinder and any entrapped air either in this excess fluid or in thewheel ,cylinder itself is thus forced to escape through the open bleedscrew.

In Figs. 6-and '1 We have shown a modification of our invention whichconcerns itself principally 'with the conduit arrangement and with thestructo the frame of the vehicle and extending along one of the sidemembers thereof to a point adjacent one of the rear wheels. A flexiblehose 8| connects conduit 80 to the lower or inlet nipple 82 of wheelcylinder 83 formed by a casting 84 having a cylinder bore 85 thereinprovided with an inlet passage 86 and an outlet passage 81.

The pistons, piston rods and attendant mechanism, may be identical withthat shown in Fig. 2. The outlet passageway 81 is providedI with anipple 88 connected to a copper conduit 89 extending along the rear axlehousing and connecting with the lower nipple of wheel cylinder 90. Theupper nipple of Wheel cylinder 90, which corresponds to wheel cylinder83, is connected to a flexible hose 9| leading to the adjacent end of acopper conduit 92 extending along one of the side members of the vehicleframe.

'Ihe forward end of the conduit 92 is connected with a flexible hose 93leading to the lower nipple of a wheel cylinder 94 located at the rightfront Wheel. Conduit 95 extends along the front axle of the vehicle andconnects the upper nipple of wheel cylinder 94 with the lower nipple ofwheel cylinder 96. The ends of conduit 95 must be flexible toaccommodate the pivoting of the front wheels. Flexible hose 91 connectsthe upper nipple of wheel cylinder 96 with copper tube 98 which extendsalong one of the side members of the frame and connects with the nipple68 which is screwed into one end of the valve member 2| as shown in Fig.4. A

As shown most clearly in Fig. 7,'the wheel cylinder casting 84 issecured to supporting pan 31a by nuts 99 associated with the inlet andoutlet nipples 82 and 88, respectively. The lower nipple is preferablymade the inlet nipple and the upper nipple theA outlet nipple, so thatany air which may ilnd its way into the cylinder will be dischargedthrough the outlet nipple by the return movement of the wheel cylinderpistons under the influence of the retractile springs 46.

The operation of this embodiment of our invention is generallysimilar'to the operation of the first embodiment. However, in theembodiment shown-in Figs. 6 and 7, a second application of the brakesreturns no fluid'to the wheel cylinder from which it has just beendischarged by the yprevious brake application, whereas, in theembodiment of Figs, 1 to 5, the small volume of fluid in each flexiblehose is returned to the Wheel cylinder from which it has just beendischarged. In Fig. 8 we have shown a wheel cylinder 83 which may beidentical in all respects with the` wheel cylinder 83. The wheelcylinder 83 is shown smaller than the wheel cylinder 83 but it should beunderstood that the wheel cylinder 83', like the wheel cylinder 83, maybe made of any desired size. The wheel cylinder 83 comprises a casting84 having a cylinder bore 85 in which is located the'pistons 45 whichmay be of the type shown in Fig. 2 or of any other desired type. Thecylinder casting 84 also provides passageways 86 and 81 which areindicated in the drawings as communicating with the cylinder bore at itsuppermost and lowermost points, respectively.

In this ligure the wheel cylinder 83 is' shown as connected to a vehiclebraking system of thel type disclosed in United States Patent No.1,841,614, of January 19, 1932, and wherein a single conduit conveysiluid under pressure from the master cylinder to the wheel cylinder andreturns fluid discharged from the wheel cylinder to the master cylinder.'I'he passageway 8E includes a threaded enlargement |00 into which isscrewed a tubular nut |0| to which is attached, by means of acompression coupling or any other suitable device, a conduit |02 whichleads to the master cylinder and forms the sole means by which iluid maybe -forced into or discharged'from the cylinder 83.

'I'he tubular nut |0| has a tapered inner end which forms a fluid sealwith the shoulder formed' at the junction of the enlarged portion of theconduit 86' with the smaller portion thereof. 'I'he passageway 81' issimilarly provided with an enlarged threaded portion |03 which is ofthesame siz'e as the threaded portion |00 of the passageway 86'. 'Thispassageway is shown as closed by a bleed screw |04 which has a solidtapered'inner One great practical advantage ofthe'type of wheel cylindershown in Figs. 7 and 8 lies inthe fact that the passageways 86, 81, 86and 81 are identical and are symmetrically disposed with I respect tothe horizontal plane passing through wheels.

the axis of the` cylinder bore. This means that where this type of wheelcylinder is .used in a system like that shown in Figs. 5 and 6, eitherpassageway may be placed at the top and asingle form of cylinder may beused for all of the vehicle Similarly, when this type of cylinder isconnected up, as shown in Fig. 8, for use in a system of the typedescribed in said Patient No. 1,841,614, or in a system of the' typeshown in Fig. 1 of this application, it is immaterial which side of thecylinder is up, and either passageway 86" or 81 may be made the upperpassageway and connected to the bleed screw. In this manner it lspossible to use a single form of cylinder for allv types ofinstallations instead of providing two or more forms of cylinders foruse in certain types of installations as has heretofore been necessary.

This feature of the wheel cylinder shown in Figs. "l and 8 is also ofparticular value where the wheel cylinders are of the two-diameter typeshown in Fig. 9. The wheel cylinder of Fig. 9 has a largev diameter |08,a smaller diameter |09 andidentical passageways ||0 and 'I'hisarrangement eliminates the necessity of providing right and left-handwheel cylinder castings and makes it possible to use a single type oftwo-diameter wheel Acylinder .casting for all vehicle wheels.

'flow of uid from said line to said master cylinder,

means for operating said master cylinder to discharge uid into saidline, Wheel cylinders con'- nected in uid communication with said line,and brake membersactuated by said wheel cylinders.

2. In a hydraulic brake systemof the class described, the combination ofa master cylinder, a reservoir therefor, means for actuating said mastercylinder to discharge uid under pressure therefrom, a line having oneend connected to said master cylinder and adapted to receive uidtherefrom, a valve in said end for preventing return ow of uid from saidline to said master cylinder, said line having a second endcommunieating with said cylinder, a valve in said second line preventingow of guid from said master cylinder into said line, wheel cylinders, aflexiblel connection between each wheel cylinder and said f line, andbrake members actuated by said wheel cylinders.

2,oc5,*o1s

scribed, the combination of a wheel cylinder-plstons reciprocabletherein, a conduit for supplying iiuid under pressure to said wheelcylinder to separate said pistons, brake members actuated by I saidpistons, normally inoperative meansvfor forcing small quantities of uidinto said. conduit. under pressure to apply the brakes, a retractile'spring for returning said pistons, a second con duit receiving' fluiddischarged from said cylinder,

a second cylinder connected to said' second conduit, pistons in saidsecond cylinder, brake elements actuated by said pistons, a-spring forreturning said last-named pistons, a third conduit receiving iiuiddischarged from said second cylinder, and a reservoir in communicationwith said third conduit.

4. In a hydraulic system of the class described, the combination of areservoir, a 'compression cylinder communicating therewith, a normallyreceiving the fluid discharged from said wheelA cylinder, said secondconduit communicating with said reservoir, said conduits being of greatlength relative to said compression cylinder and reservoir for saidcylinder, a conduit connected to said cylinder, a valve preventing ow ofuid from said conduit to said cylinder, an actuating cylinder connectedto said conduit, a piston reciprocably mountedinl said, actuatingcylinder,

means 'actuated by-said piston, a second conduit connecting saidcylinders, and a valve in said i second conduit preventing ow of uidfrom saidv first-mentioned cylinder to said conduit.

6. In a vehicle having a frame and front and Vrear wheels movablerelative thereto, the combination of a fluid reservoir, a mastercylinder communicating with said reservoir, a pipe line forming acircuit and attached to said frame, said pipe line having two ends, bothof which communicate with said cylinder, a wheel cylinderl located ateach wheel of the vehicle, a exible *hose connecting each wheel cylinderwith said pipe line, and braking means actuated by said along both ofsaid frame members and across each end of said frame, means connectingsaid uid line with Isaid compression cylinder. a wheel cylinder at eachvehicle wheel, said cylinders `being located ,beneath said uid line, aexible hose extending in a generally upward direction and connectingeach wheel cylinder with said fluid line, and brake members actuatedby,said wheel cylinders. u

8. In a vehicle having a frame including side rails, axles movablerelative to saidframe, and

wheels associated with said ax1es,the combinau tion of a fluidreservoir, a uid compressor, means for intermittently actuating'saidcompressor, said compressor being connected to said ond wheel cylinderlocated at the opposite wheel,

said second conduit connected to said second wheel cylinder andextending along the axle connecting said wheels, a second flexible hoseconnected to said second wheel cylinder, a third conduit extending alongthe vehicle frame and leading back to said compressor, said second hoseconnected to said third conduit, and brake mechanism actuated by saidwheel cylinders.

. 9. In a hydraulic brake system, the combination of a compressor andreservoir unit, a circulatory iluid line having one end connected withsaid unit to receive-fluid therefrom and a second end connected to said'unit to return fluid thereto, wheel cylinders connected to said fluidline at intervals spaced therealong, brake mechanism actuated by saidwheel cylinders, and means for operating said compressor only duringperiods of brake application. Y

10. In a fluid system of the class-described, the combination of a fluidcompressor, means for actuating said compressor, a circulatory iluidconduit having a fluid capacity less than the volumetric change of saidchamber, and a reservoir. connected to said fluid compressor.

11. In hydraulic brake mechanism of the class described, the combinationof a reservoir, a fluid compressor communicating therewith, means foractuating said fluid compressor, a conduit receiving at spacedintervals'fluid discharged by said compressor, a wheel cylinderconnected to said conduit, pistons reciprocably mounted in said wheelcylinder, a second conduit receiving the fluid discharged from saidcylinder by return movement of said pistons, said'second conduit beingof copper, means for returning said pistons, and brake mechanismactuated by said pistons.

12. In mechanism of the class described, the combination of a wheelcylinder having a cylin- 'der bore, a passageway connected to the top ofsaid bore, means for supplying fluid to said cylinder bore through saidpassageway, a bleed passageway communicating with said cylinder bore ata point below the point vof communication between said first-namedpassageway. and said cylinder bore, means normally closing said bleedpassageway, pistons reciprocably mounted in said cylinder, and brakemeans actuated by said pistons.

13. In mechanism of the class described, the combination of a cylinderhaving a bore therein, ,pistons reciprocably mounted in said bore, saidpistons having plane faces and being provided with annular groovesspaced from said faces, sealing means in said grooves, brake membersconnected to said pistons, means normally hold- \in'g said pistons withtheir plane faces in engage- Yment, and means for supplying liquid underpressure to said cylinder.

1 4. In mechanism of the class described, the

combination of a uid compressor part, a reservoir part, said compressorpart communicating with said reservoir part, a conduit connected to saidcompressor and receiving the fluid discharged therefrom, an actuatingcylinder having a single fluid chamber, an inlet passagewaycommunicating with the lower portion of. said chamber, a connectionbetween said conduit and said inlet passageway, an outlet passagewaycommunicating with the upper portion of said chamber, a second conduitconnected` to said outlet passageway and communicating with one of saidparts, a piston in said cylinder chamber, valve means preventing reverseflow through said inlet and outlet passages and a brake element actuatedby said piston.

15. In mechanism of the class described, the combination of va fluidcompressor, a wheel cylinder having a single fluid chamber, inlet andoutlet passageways communicating with lower and upper portions of saidchamber, respectively, said passageways lying in the same verticalplane, means connecting said passageways with said fluid compressor,means preventing reverse flow through said inlet and outlet passages,pistons in said wheel cylinder, brake mechanism actuated by saidpistons, a reservoir communicating with said fluid compressor, Vandmeans for actuating said fluid compressor.

16. In a hydraulic brake system of theclass described, the combinationof a fluidl reservoir, a fluid compressor communicating therewith,means, including a pedal, for actuating said fluid compressor, wheelcylinders mounted for movement relative to said compressor, a metallicpipe line having two ends, vboth of said ends being connected to saidcompressor, flexible rubber hoses connecting said wheel cylinders withsaid metallic pipe line, and means actuated by said wheel cylinders. f

17. In an automotive Vehicle having a frame and wheels movable relativeto said frame, the combination `of a reservoir, a fluid compressorsupplied from said reservoir, means mounting said compressor andreservoir on said frame, a brake pedal and connections for actuatingsaid compressor, a pipe line forming a closed loop about said frame andhaving two ends, both of which are connected to said compressor, wheelcylinders mounted at the vehicle wheels, pistons .in said wheelcylinders, a brake drum associated with each wheel, brake shoes moved bysaid pistons into engagement with said brake drums, retractile springsfor returning said brake shoes and pistons, each wheel cylinderreceiving an additional volume of fluid upon each application of allfluid discharged therefrom, said pipe line being of great lengthrelative to said compressor, means l for operating said compressor todischarge fluid into said pipe line,'a branch pipe line capable ofholding only a relatively small volume of fluid, an actuating cylinderconnected to said branch line, a piston reciprocable in said actuatingcylinder, said cylinder capable of holding a relatively large volume offluid when said piston-is in one of its positions, means actuated bysaid piston',v and means for returning said piston.

19, In a hydraulic system of the class described,

the combination of a i'luid compressor, means to operate said compressorintermittently, a rst charged from said rst-mentioned actuating cylinderby return of the piston therein and conveying said uid towardgsai'dsecond actuating cylinder, a piston in said second actuating cylinder,means yoperated by said last-named piston, means for returning saidlast-named piston, and a third conduit communicating with said secondactuating cylinder for receiving fluid discharged therefrom andconveying said uid toward said compressor.

20. In a hydraulic brake system, the combination of a wheel cylinderhaving a" cylinder bore and identical passageways communicating withsaid cylinder bore at its uppermost andlowermost points, piston meansreciprocable in said bore, a bleed screw associated with. and normallyclosing the passageway communicating with the uppermost point of saidcylinder bore, and. conduit means connected to the passagewaycommunicatingwith the lowermost point .of said cylinder bore.

21. In a motor cylinder of the class' described,

the combination of means providing a cylinder bore and identicalpassageways communicating with said bore at points equally spaced in avertical piane from the axis of said bore, weeding meansnormally closingone of. said-passageways,

Y and conduit means connected to the other of said passageways andthrough which uid under pressure is supplied to said cylinder.

22. In hydraulic brake mechanism of the class described, the combinationof supply means including a uid reservoir and a uid compressor suppliedtherefrom, operator controlled means for actuating said iiuidcompressor, a conduit receiving the iiuid discharged by said compressor,a uid motor connected to said conduit, brake mechanism actuated by saidmotor, a second conduit receivingv the uid discharged from said motorand returning said iluid to said supply means, and means other than saidreservoir for maintaining the uid in said conduits'and motor undersuperatmospheric pressur'e between operating intervals of saidcompressor.

23. In brake mechanism of the class described,

v'the combination of a supply unit comprising a reservoir and liuidcompressor, means for actuating said uid compressor at spaced intervals,a single conduit receiving all fluid discharged .by said compressorfamotor cylinder connected to said conduit, a piston reciprocably mountedin said motor cylinder, brake mechanism operated by said piston, asecond conduit receiving the fluid discharged from said cylinder byreturn movement of said piston, said second conduit returning said fluidto said unit, said conduits being of. great length relative to saidsupply unit and being separate and distinct throughout thegreaterportions of their lengths, and means for maintaining saidconduits and motor cylinder completely lled with fluid while saidcompressor is idle.

WALLACE F. OLIVER.

HERBERT C. BOWEN.

ERWIN F. LOWEKE.

